There is little biological data available for diving birds because many live in hard-to-study, remote habitats. Only one species of diving bird, the black-footed penguin (Spheniscus demersus), has been studied in respect to auditory capabilities (Wever et al. 1969). We therefore measured in-air auditory threshold in ten species of diving birds, using the auditory brainstem response (ABR). The average audiogram obtained for each species followed the U-shape typical of birds and many other animals. All species tested shared a common region of greatest sensitivity, from 1000 to 3000 Hz, although audiograms differed significantly across species. Thresholds of all duck species tested were more similar to each other than to the two non-duck species tested. The red-throated loon (Gavia stellata) and northern gannet (Morus bassanus) exhibited the highest thresholds while the lowest thresholds belonged to the duck species, specifically the lesser scaup (Aythya affinis) and ruddy duck (Oxyura jamaicensis). Vocalization parameters were also measured for each species, and showed that with the exception of the common eider (Somateria mollisima), the peak frequency, i.e. frequency at the greatest intensity, of all species’ vocalizations measured here fell between 1000 and 3000 Hz, matching the bandwidth of the most sensitive hearing range.

This study investigated diel changes in ambient noise levels and the number of whistles produced by bottlenose dolphins (Tursiops truncatus) at the Brookfield Zoo in Brookfield, Illinois. Automated, continuous 24-h underwater recordings were made from 1 January to 31 March 2008. The number of whistles, types of whistles, and background noise level were examined for each hour. Nine distinct frequency contours were identified, named, and analyzed for minimum frequency, maximum frequency, peak frequency, and duration.Since all pumps and filters at the Seven Seas Exhibit of Brookfield Zoo were housed in a separate building isolated from the dolphins' pools, background noise was relatively low and consistent throughout the day (95 to 98 dB re: 1 µPa). However, when the zoo staff used a scrubber to clean the pool walls, the background noise was higher and fluctuated (up to 112 dB re: 1 µPa). The dolphins whistled significantly less during these scrubbing periods.The dolphins exhibited a distinct diel pattern in whistle production. Increased whistle production coincided with increased interactions with humans during feeding/training sessions; the number of whistles peaked in the late afternoon (~1600 h) and then quickly tapered off throughout the night.The investigation began with eight dolphins; however, the death of one young male and the transport of two adult males to another facility left five dolphins: two adult females and two juvenile females along with an unrelated young male. These changes provided an opportunity to explore how social change affected whistle production.After the two adult males were transported out of the facility, two of the distinct whistle types disappeared, suggesting that each of the two dolphins had a unique whistle type. The results of this investigation highlight the usefulness of passive recording for monitoring ambient noise, as well as for documenting the activity pattern and social interactions of captive bottlenose dolphins.

Auditory sensitivity was measured in a species of diving duck that is not often kept in captivity, the lesser scaup. Behavioral (psychoacoustics) and electrophysiological [the auditory brainstem response (ABR)] methods were used to measure in-air auditory sensitivity, and the resulting audiograms were compared. Both approaches yielded audiograms with similar U-shapes and regions of greatest sensitivity (2000À3000 Hz). However, ABR thresholds were higher than psychoacoustic thresholds at all frequencies. This difference was least at the highest frequency tested using both methods (5700 Hz) and greatest at 1000 Hz, where the ABR threshold was 26.8 dB higher than the behavioral measure of threshold. This difference is commonly reported in studies involving many different species. These results highlight the usefulness of each method, depending on the testing conditions and availability of the animals. [http://dx

Lesser scaup (Aythya affinis) are a species of diving duck that dive to depths of greater than 20 m to forage on crustaceans, mollusks, and fish. Currently, there are no measures of underwater hearing of any diving bird because of the inherent difficulties of training a bird to respond to sound underwater. Lesser scaup in a captive colony at USGS Patuxent Wildlife Research Center in Laurel, MD are being trained to participate in in-air and underwater behavioral audiograms. Ducklings were hand-reared to respond to trainers, auditory signals, and mealworm rewards. The ducks were then trained on a go/no-go task to respond to varying frequencies and intensity levels by pecking an LED-lit target. All targets and acquisition devices were designed to follow similar procedures in-air and underwater. Previous auditory brainstem response (ABR) tests demonstrated an in-air maximum sensitivity at 2–3 kHz. These behavioral audiograms will provide a measure to compare ABR and psychoacoustic thresholds as well as a measure of underwater thresholds, which would be difficult to implement using only the ABR.

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